Over 50,000 lives are lost annually due to colon cancer, making it the third deadliest cancer in the United States. The aim of this project is to improve early-stage colon cancer screening using a unique Raman imaging microendoscope to detect molecularly targeted nanoparticles. A scanning Raman endoscope device capable of fast non-contact imaging will be built and used to image targeted silica-encapsulated, gold-based nanoparticles. The particles produce a Raman light scattering signal and will be administered topically to the colon in mixtures that enable ratiometric imaging to subtract out background signal from that targeted particles. The Raman endoscope, using laser light, illuminates the nanoparticles and detects the inelastically scattered light. We will fabricate the circumferential-scanning Raman endoscope to image the colon anatomy with white light as well as colon cancer biomarkers with targeted Raman-active particles. The Raman endoscope has been designed for clinical use but will be evaluated with spontaneous tumors (Pirc rats) and primary human xenografts. De-identified human colon cancer tissues will be procured during routine colonoscopy and surgically implanted into animals. Overexpression of various colon cancer biomarkers will be assessed on these human colon cancer tissues using qPCR, western blot analysis and immunohistochemistry. Selected tumor-targeting ligands, will be used to functionalize the surface of our Raman nanoparticle contrast agents. We will assess tumor targeting efficiency and the performance of our Raman endoscope first in rats and then in large animals (porcine). Although this novel diagnostic strategy is not limited to the colon, we are motivated to validate our approach with colorectal cancer due to the availability of tumor-targeting ligands, endoscope compatibility, reduced toxicity and a real need for improved detection of this malignancy. The approach is expected to be low risk because Raman endoscopes have previously been used in humans and because gold based nanoparticles are relatively inert with some constructs already approved by the FDA. Harnessing the ultrasensitive detection and multiplexing capabilities of Raman spectroscopy for the detection of cancer could serve as a powerful diagnostic tool with the potential to significantly impact the survival rate of cancer patients by earlier cancer detection.